The Education Department’s Office for Civil Rights has begun dismissing hundreds of civil rights complaints under a new protocol that allows investigators to disregard cases that are part of serial filings or that they consider burdensome to the office.

Department officials said the new policy targeted advocates who flooded the office with thousands of complaints for similar violations, jamming its investigation pipeline with cases that could be resolved without exhausting staff and resources. But civil rights advocates worry that the office’s rejection of legitimate claims is the most obvious example to date of its diminishing role in enforcing civil rights laws in the nation’s schools.

Liz Hill, a spokeswoman for the Education Department, said the new provision was part of the office’s revision of its manual that lays out procedures for processing civil rights cases. The goal of the new manual, which took effect last month, is to help the office better manage its docket, investigations and resolutions, she said.

Among the changes implemented immediately is a provision that allows the Office for Civil Rights to dismiss cases that reflect “a pattern of complaints previously filed with O.C.R. by an individual or a group against multiple recipients,” or complaints “filed for the first time against multiple recipients that” place “an unreasonable burden on O.C.R.’s resources.”

So far, the provision has resulted in the dismissal of more than 500 disability rights complaints.

Catherine E. Lhamon, who led the Office for Civil Rights under the Obama administration, said the new provision undermined the mission of the office. Unlike the Justice Department, the Education Department cannot pick and choose the cases it pursues. If the office has evidence that the law has been violated, it must open a case.

“The thing that scares me is when they get to say ‘we won’t open some cases because it’s too much for us,’ or ‘we don’t like complainant,’ or ‘it’s not our week to work on that,’ you start to change the character of the office,” Ms. Lhamon said.

But Debora L. Osgood, a lawyer who worked for 25 years at the Office for Civil Rights and now consults with and represents schools on civil rights matters, praised the change. She said the provision showed that the agency was “essentially taking the reins back for control of its complaint docket.”

Ms. Osgood said that in her experience, one person could clog the pipeline in each of the agency’s 12 regional offices, limiting investigators’ ability to respond to other complaints. It often frustrated investigators who prided themselves on being able to resolve complaints promptly, she said.